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Q.

A carton of 24 bulbs contain 6 defective bulbs. 1 bulb is drawn at random. If the bulb selected is defective and it is not replaced and a second bulb is selected at random from the rest, then from the options given below, what is the probability that the second bulb is defective?


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a

5 23

b

3 4

c

5 24

d

3 5  

answer is A.

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Detailed Solution


It is given that, a carton consists of 24 bulbs containing 6 defective bulb.
We have to find the probability that the bulb is not defective.
There is a total of 24 bulbs in which 6 are defective, that means,
246=18 are non-defective.
So, the total number of outcomes is 24 .
Let A be the event that the bulb is not defective. Then,
P(A)= Number of favourable outcomes Total number of outcomes .
= 18 24
= 3 4
Obtain the probability that the 2nd bulb is defective.
If the selected bulb is defective and not replaced, then the number of defective bulbs left in a cartoon is
241=23
Out of which 5 are defective since 1 defective bulb is already drawn out.
Let B be the event that the 2nd bulb is defective. Then,
P(B)= Number of favourable outcomes Total number of outcomes .
= 5 23
The probability that the 2nd bulb is defective is 5 23 .
Hence option 1) is correct.
 
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